Pitch-based carbon foam and composites

ABSTRACT

A process for producing carbon foam or a composite is disclosed which obviates the need for conventional oxidative stabilization. The process employs mesophase or isotropic pitch and a simplified process using a single mold. The foam has a relatively uniform distribution of pore sizes and a highly aligned graphic structure in the struts. The foam material can be made into a composite which is useful in high temperature sandwich panels for both thermal and structural applications.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] The United States Government has rights in this inventionpursuant to contract No. DE-AC05-96OR22464 between the United StatesDepartment of Energy and Lockheed Martin Energy Research Corporation.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to carbon foam and composites, andmore particularly to a process for producing them.

[0003] The extraordinary mechanical properties of commercial carbonfibers are due to the unique graphitic morphology of the extrudedfilaments. See Edie, D. D., “Pitch and Mesophase Fibers,” in CarbonFibers, Filaments and Composites, Figueiredo (editor), Kluwer AcademicPublishers, Boston, pp. 43-72 (1990). Contemporary advanced structuralcomposites exploit these properties by creating a disconnected networkof graphitic filaments held together by an appropriate matrix. Carbonfoam derived from a pitch precursor can be considered to be aninterconnected network of graphitic ligaments or struts, as shown inFIG. 1. As such interconnected networks, they represent a potentialalternative as a reinforcement in structural composite materials.

[0004] Recent developments of fiber-reinforced composites has beendriven by requirements for improved strength, stiffness, creepresistance, and toughness in structural engineering materials. Carbonfibers have led to significant advancements in these properties incomposites of various polymeric, metal, and ceramic matrices.

[0005] However, current applications of carbon fibers has evolved fromstructural reinforcement to thermal management in application rangingfrom high density electronic modules to communication satellites. Thishas simulated research into novel reinforcements and compositeprocessing methods. High thermal conductivity, low weight, and lowcoefficient of thermal expansion are the primary concerns in thermalmanagement applications. See Shih, Wei, “Development of Carbon-CarbonComposites for Electronic Thermal Management Applications,” IDAWorkshop, May 3-5, 1994, supported by AF Wright Laboratory underContract Number F33615-93-C-2363 and AR Phillips Laboratory ContractNumber F29601-93-C-0165 and Engle, G. B., “High Thermal Conductivity C/CComposites for Thermal Management,” IDA Workshop, May 3-5, 1994,supported by AF Wright Laboratory under Contract F33615-93-C-2363 and ARPhillips Laboratory Contract Number F29601-93-C-0165. Such applicationsare striving towards a sandwich type approach in which a low densitystructural core material (i.e. honeycomb or foam) is sandwiched betweena high thermal conductivity facesheet. Structural cores are limited tolow density materials to ensure that the weight limits are not exceeded.Unfortunately, carbon foams and carbon honeycomb materials are the onlyavailable materials for use in high temperature applications (>1600°C.). High thermal conductivity carbon honeycomb materials are extremelyexpensive to manufacture compared to low conductivity honeycombs,therefore, a performance penalty is paid for low cost materials. Highconductivity carbon foams are also more expensive to manufacture thanlow conductivity carbon foams, in part, due to the starting materials.order to produce high stiffness and high conductivity carbon foams,invariably, a pitch must be used as the precursor. This is because pitchis the only precursor which forms a highly aligned graphitic structurewhich is a requirement for high conductivity. Typical processes utilizea blowing technique to produce a foam of the pitch precursor in whichthe pitch is melted and passed from a high pressure region to a lowpressure region. Thermodynamically, this produces a “Flash,” therebycausing the low molecular weight compounds in the pitch to vaporize (thepitch boils), resulting in a pitch foam. See Hagar, Joseph W. and Max L.Lake, “Novel Hybrid Composites Based on Carbon Foams,” Mat. Res. Soc.Symp., Materials Research Society, 270:29-34 (1992), Hagar, Joseph W.and Max L. Lake, “Formulation of a Mathematical Process Model ProcessModel for the Foaming of a Mesophase Carbon Precursor,” Mat. Res. Soc.Symp., Materials Research Society, 270:35-40 (1992), Gibson, L. J. andM. F. Ashby, Cellular Solids: Structures & Properties, Pergamon Press,New York (1988), Gibson, L. J., Mat. Sci. and Eng A110, 1 (1989),Knippenberg and B. Lersmacher, Phillips Tech. Rev., 36(4), (1976), andBonzom, A., P. Crepaux and E. J. Moutard, U.S. Pat. No. 4,276,246,(1981). Then, the pitch foam must be oxidatively stabilized by heatingin air (or oxygen) for many hours, thereby, cross-linking the structureand “setting” the pitch so it does not melt during carbonization. SeeHagar, Joseph W. and Max L. Lake, “Formulation of a Mathematical ProcessModel Process Model for the Foaming of a Mesophase Carbon Precursor,Mat. Res. Soc. Symp., Materials Research Society, 270:35-40 (1992) andWhite, J. L., and P. M. Shaeffer, Carbon, 27:697 (1989). This is a timeconsuming step and can be an expensive step depending on the part sizeand equipment required. The “set” or oxidized pitch is then carbonizedin an inert atmosphere to temperatures as high as 1100° C. Then,graphitization is performed at temperatures as high as 3000° C. toproduce high thermal conductivity graphitic structure, resulting in astiff and very thermally conductive foam.

[0006] Other techniques utilize a polymeric precursor, such as phenolic,urethane, or blends of these with pitch. See Hagar, Joseph W. and Max L.Lake, “Idealized Strut Geometries for Open-Celled Foams,” Mat. Res. Soc.Symp., Materials Research Society, 270:41-46 (1992), Aubert, J. W., (MRSSymposium Proceedings, 207:117-127 (1990), Cowlard, F. C. and J. C.Lewis, J. of Mat. Sci., 2:507-512 (1967) and Noda, T., Inagaki and S.Yamada, J. of Non-Crystalline Solids, 1:285-302, (1969). High pressureis applied and the sample is heated. At a specified temperature, thepressure is released, thus causing the liquid to foam as volatilecompounds are released. The polymeric precursors are cured and thencarbonized without a stabilization step. However, these precursorsproduce a “glassy” or vitreous carbon which does not exhibit graphiticstructure and, thus, has low thermal conductivity and low stiffness. SeeHagar, Joseph W. and Max L. Lake, “Idealized Strut Geometries forOpen-Celled Foams,” Mat. Res. Soc. Symp., Materials Research Society,270:41-46 (1992).

[0007] In either case, once the foam is formed, it is then bonded in aseparate step to the facesheet used in the composite. This can be anexpensive step in the utilization of the foam.

[0008] The process of this invention overcomes these limitations, by notrequiring a “blowing” or “pressure release” technique to produce thefoam. Furthermore, an oxidation stabilization step is not required, asin other methods used to produce pitch-based carbon foams with a highlyaligned graphitic structure. This process is less time consuming, andtherefore, will be lower in cost and easier to fabricate.

[0009] Lastly the foam can be produced with an integrated sheet of highthermal conductivity carbon on the surface of the foam, therebyproducing a carbon foam with a smooth sheet on the surface to improveheat transfer.

SUMMARY OF THE INVENTION

[0010] The general object of the present invention is to provide carbonfoam and a composite from a mesophase or isotropic pitch such assynthetic, petroleum or coal-tar based pitch.

[0011] Another object is to provide a carbon foam and a composite frompitch which does not require an oxidative stabilization step.

[0012] These and other objectives are accomplished by a method ofproducing carbon foam wherein an appropriate mold shape is selected andpreferably an appropriate mold release agent is applied to walls of themold. Pitch is introduced to an appropriate level in the mold, and themold is purged of air such as by applying a vacuum. Alternatively, aninert fluid could be employed. The pitch is heated to a temperaturesufficient to coalesce the pitch into a liquid which preferably is ofabout 50° C. to about 100° C. above the softening point of the pitch.The vacuum is released and an inert fluid applied at a static pressureup to about 1000 psi. The pitch is heated to a temperature sufficient tocause gases to evolve and foam the pitch. The pitch is further heated toa temperature sufficient to coke the pitch and the pitch is cooled toroom temperature with a simultaneous and gradual release of pressure.

[0013] In another aspect, the previously described steps are employed ina mold composed of a material such that the molten pitch does not wet.

[0014] In yet another aspect, the objectives are accomplished by thecarbon foam product produced by the methods disclosed herein including afoam product with a smooth integral facesheet.

[0015] In still another aspect a carbon foam composite product isproduced by adhering facesheets to a carbon foam produced by the processof this invention.

DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a micrograph illustrating typical carbon foam withinterconnected carbon ligaments and open porosity.

[0017] FIGS. 2-6 are micrographs of pitch-derived carbon foamgraphitized at 2500° C. and at various magnifications.

[0018]FIG. 7 is a SEM micrograph of the foam produced by the process ofthis invention.

[0019]FIG. 8 is a chart illustrating cumulative intrusion volume versuspore diameter.

[0020]FIG. 9 is a chart illustrating log differential intrusion volumeversus pore diameter.

[0021]FIG. 10 is a graph illustrating the temperatures at whichvolatiles are given off from raw pitch.

[0022]FIG. 11 is an X-ray analysis of the graphitized foam produced bythe process of this invention.

[0023] FIGS. 12 A-C are photographs illustrating foam produced withaluminum crucibles and the smooth structure or face sheet that develops.

[0024]FIG. 13A is a schematic view illustrating the production of acarbon foam composite made in accordance with this invention.

[0025]FIG. 13B is a perspective view of the carbon foam composite ofthis invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] In order to illustrate the carbon foam product and composite ofthis invention, the following Examples are set forth. They are notintended to limit the invention in any way.

EXAMPLE I

[0027] Pitch powder, granules, or pellets are placed in a mold with thedesired final shape of the foam. These pitch materials can be solvatedif desired. In this Example Mitsubishi ARA-24 mesophase pitch wasutilized. A proper mold release agent or film is applied to the sides ofthe mold to allow removal of the part. In this case, Boron Nitride sprayand Dry Graphite Lubricant were separately used as a mold release agent.If the mold is made from pure aluminum, no mold release agent isnecessary since the molten pitch does not wet the aluminum and, thus,will not stick to the mold. Similar mold materials may be found that thepitch does not wet and, thus, they will not need mold release. Thesample is evacuated to less than 1 torr and then heated to a temperatureapproximately 50 to 100° C. above the softening point. In this casewhere Mitsubishi ARA24 mesophase pitch was used, 300° C. was sufficient.At this point, the vacuum is released to a nitrogen blanket and then apressure of up to 1000 psi is applied. The temperature of the system isthen raised to 800° C., or a temperature sufficient to coke the pitchwhich is 500° C. to 1000° C. This is performed at a rate of no greaterthan 5° C./min. and preferably at about 2° C./min. The temperature isheld for at least 15 minutes to achieve an assured soak and then thefurnace power is turned off and cooled to room temperature. Preferablythe foam was cooled at a rate of approximately 1.5° C./min. with releaseof pressure at a rate of approximately 2 psi/min. Final foamtemperatures for three product runs were 500° C., 630° C. and 800° C.During the cooling cycle, pressure is released gradually to atmosphericconditions. The foam was then heat treated to 1050° C. (carbonized)under a nitrogen blanket and then heat treated in separate runs to 2500°C. and 2800° C. (graphitized) in Argon.

[0028] Carbon foam produced with this technique was examined withphotomicrography, scanning electron microscopy (SEM), X-ray analysis,and mercury porisimetry. As can be seen in the FIGS. 2-7, theinterference patterns under cross-polarized light indicate that thestruts of the foam are completely graphitic. That is, all of the pitchwas converted to graphite and aligned along the axis of the struts.These struts are also similar in size and are interconnected throughoutthe foam. This would indicate that the foam would have high stiffnessand good strength. As seen in FIG. 7 by the SEM micrograph of the foam,the foam is open cellular meaning that the porosity is not closed. FIGS.8 and 9 are results of the mercury porisimetry tests. These testsindicate that the pore sizes are in the range of 90-200 microns.

[0029] A thermogravimetric study of the raw pitch was performed todetermine the temperature at which the volatiles are evolved. As can beseen in FIG. 11, the pitch loses nearly 20% of its mass fairly rapidlyin the temperature range between about 420° C. and about 480° C.Although this was performed at atmospheric pressure, the addition of1000 psi pressure will not shift this effect significantly. Therefore,while the pressure is at 1000 psi, gases rapidly evolved during heatingthrough the temperature range of 420° C. to 480° C. The gases produce afoaming effect (like boiling) on the molten pitch. As the temperature isincreased further to temperatures ranging from 500° C. to 1000° C.(depending on the specific pitch), the foamed pitch becomes coked (orrigid), thus producing a solid foam derived from pitch. Hence, thefoaming has occurred before the release of pressure and, therefore, thisprocess is very different from previous art.

[0030] Samples from the foam were machined into specimens for measuringthe thermal conductivity. The bulk thermal conductivity ranged from 58W/m·K to 106 W/m·K. The average density of the samples was 0.53 g/cm³.When weight is taken into account, the specific thermal conductivity ofthe pitch derived foam is over 4 times greater than that of copper.Further derivations can be utilized to estimate the thermal conductivityof the struts themselves to be nearly 700 W/m·K. This is comparable tohigh thermal conductivity carbon fibers produced from this same ARA24mesophase pitch.

[0031] X-ray analysis of the foam was performed to determine thecrystalline structure of the material. The x-ray results are shown inFIG. 11. From this data, the graphene layer spacing (d₀₀₂) wasdetermined to be 0.336 nm. The coherence length (La, 1010) wasdetermined to be 203.3 nm and the stacking height was determined to be442.3 nm.

[0032] The compression strength of the samples were measured to be 3.4MPa and the compression modulus was measured to be 73.4 MPa. The foamsample was easily machined and could be handled readily without fear ofdamage, indicating a good strength.

[0033] It is important to note that when this pitch is heated in asimilar manner, but under only atmospheric pressure, the pitch foamsdramatically more than when under pressure. In fact, the resulting foamis so fragile that it could not even be handled to perform tests.

EXAMPLE II

[0034] An alternative to the method of Example I is to utilize a moldmade from aluminum. In this case two molds were used, an aluminumweighing dish and a sectioned soda can. The same process as set forth inExample I is employed except that the final coking temperature was only630° C., so as to prevent the aluminum from melting.

[0035]FIG. 12 A-C illustrate the ability to utilized complex shapedmolds for producing complex shaped foam. In one case, shown in FIG. 12 Athe top of a soda can was removed and the remaining can used as a mold.No release agent was utilized. Note that the shape of the resulting partconforms to the shape of the soda can, even after graphitization to2800° C. This demonstrates the dimensional stability of the foam and theability to produce near net shaped parts.

[0036] In the second case, as shown in FIGS. 12 B and C employing analuminum weight dish, a very smooth surface was formed on the surfacecontacting the aluminum. This is directly attributable to the fact thatthe molten pitch does not wet the surface of the aluminum. This wouldallow one to produce complex shaped parts with smooth surfaces so as toimprove contact area for bonding or improving heat transfer. This smoothsurface will act as a face sheet and, thus, a foam-core composite can befabricated in-situ with the fabrication of the face sheet. Since it isfabricated together and an integral material no interface joints result,thermal stresses will be less, resulting in a stronger material.

[0037] The following examples illustrate the production of a compositematerial employing the foam of this invention.

EXAMPLE III

[0038] Pitch derived carbon foam was produced with the method describedin Example I. Referring to FIG. 13A the carbon foam 10 was then machinedinto a block 2″×2″×½″. Two pieces 12 and 14 of a prepeg comprised ofHercules AS4 carbon fibers and ICI Fibirite Polyetheretherkeytonethermoplastic resin also of 2″×2″×½″ size were placed on the top andbottom of the foam sample, and all was placed in a matched graphite mold16 for compression by graphite plunger 18. The composite sample washeated under an applied pressure of 100 psi to a temperature of 380° C.at a rate of 5° C./min. The composite was then heated under a pressureof 100 psi to a temperature of 650° C. The foam core sandwich panelgenerally 20 was then removed from the mold and carbonized undernitrogen to 1050° C. and then graphitized to 2800° C., resulting in afoam with carbon-carbon facesheets bonded to the surface. The compositegenerally 30 is shown in FIG. 13B.

EXAMPLE IV

[0039] Pitch derived carbon foam was produced with the method describedin Example I. It was then machined into a block 2″×2″×½. Two pieces ofcarbon-carbon material, 2″×2″×½, were coated lightly with a mixture of50% ethanol, 50% phenolic Durez© Resin available from OccidentalChemical Co. The foam block and carbon-carbon material were positionedtogether and placed in a mold as indicated in Example III. The samplewas heated to a temperature of 150° C. at a rate of 5° C./min and soakedat temperature for 14 hours. The sample was then carbonized undernitrogen to 1050° C. and then graphitized to 2800° C., resulting in afoam with carbon-carbon facesheets bonded to the surface. This is alsoshown generally at 30 in FIG. 13B.

EXAMPLE V

[0040] Pitch derived carbon foam was produced with the method describedin Example I. The foam sample was then densified with carbon by themethod of chemical vapor infiltration for 100 hours. The densityincreased to 1.4 g/cm³, the flexural strength was 19.5 MPa and theflexural was 2300 MPa. The thermal conductivity of the raw foam was 58W/m·K and the thermal conductivity of the densified foam was 94 W/m·K.

EXAMPLE VI

[0041] Pitch derived carbon foam was produced with the method describedin Example I. The foam sample was then densified with epoxy by themethod of vacuum impregnation. The epoxy was cured at 150° C. for 5hours. The density increased to 1.37 g/cm³ and the flexural strength wasmeasured to be 19.3 MPa.

[0042] It is obvious that other materials, such as metals, ceramics,plastics, or fiber reinforced plastics could be bonded to the surface ofthe foam of this invention to produce a foam core composite materialwith acceptable properties. It is also obvious that ceramics, or glass,or other materials could be impregnated into the foam for densification.

[0043] Based on the data taken to date from the carbon foam material,several observations can be made and the important features of theinvention are:

[0044] 1. Pitch-based carbon foam can be produced without an oxidativestabilization step, thus saving time and costs.

[0045] 2. High graphitic alignment in the struts of the foam is achievedupon graphitization to 2500° C., and thus high thermal conductivity andstiffness will be exhibited by the foam, making them suitable as a corematerial for thermal applications.

[0046] 3. High compressive strengths should be achieved with mesophasepitch-based carbon foams, making them suitable as a core material forstructural applications.

[0047] 4. Foam core composites can be fabricated at the same time as thefoam is generated, thus saving time and costs.

[0048] 5. Rigid monolithic preforms can be made with significant openporosity suitable for densification by the Chemical Vapor Infiltrationmethod of ceramic and carbon infiltrants.

[0049] 6. Rigid monolithic preforms can be made with significant openporosity suitable for activation, producing a monolithic activatedcarbon.

[0050] 7. It is obvious that by varying the pressure applied, the sizeof the bubbles formed during the foaming will change and, thus, thedensity, strength, and other properties can be affected.

[0051] The following alternative procedures and products can also beeffected by the process of this invention:

[0052] 1. Fabrication of preforms with complex shapes for densificationby CVI or Melt Impregnation.

[0053] 2. Activated carbon monoliths.

[0054] 3. Optical absorbent.

[0055] 4. Low density heating elements.

[0056] 5. Firewall Material.

[0057] 6. Low secondary electron emission targets for high-energyphysics applications.

[0058] It will thus be seen that the present invention provides for themanufacture of pitch-based carbon foam for structural and thermalcomposites. The process involves the fabrication of a graphitic foamfrom a mesophase or isotropic pitch which can be synthetic, petroleum,or coal-tar based. A blend of these pitches can also be employed. Thesimplified process utilizes a high pressure high temperature furnace andthereby, does not require and oxidative stabilization step. The foam hasa relatively uniform distribution of pore sizes (≈100 microns), verylittle closed porosity, and density of approximately 0.53 g/cm³. Themesophase pitch is stretched along the of the foam structure and therebyproduces a highly aligned graphitic structure in the struts. Thesestruts will exhibit thermal conductivities and stiffness similar to thevery expensive high performance carbon fibers (such as P-120 and K1100).Thus, the foam will exhibit high stiffness and thermal conductivity at avery low density (≈0.5 g/cc). This foam can be formed in place as a corematerial for high temperature sandwich panels for both thermal andstructural applications, thus reducing fabrication time.

[0059] By utilizing an isotropic pitch, the resulting foam can be easilyactivated to produce a high surface area activated carbon. The activatedcarbon foam will not experience the problems associated with granulessuch as attrition, channeling, and large pressure drops.

What is claimed is:
 1. A process of producing carbon foam comprising:selecting an appropriate mold shape; introducing pitch to an appropriatelevel in a mold; purging air from the mold; heating the pitch to atemperature sufficient to coalesce the pitch into a liquid; releasingthe vacuum and applying an inert fluid at a static pressure up to about1000 psi; heating the pitch to a temperature sufficient to cause gasesto evolve and foam the pitch; heating the pitch to a temperaturesufficient to coke the pitch; and cooling the foam to room temperaturewith a simultaneous release of pressure.
 2. The process of claim 1wherein the pitch is introduced as granulated pitch.
 3. The process ofclaim 1 wherein the pitch is introduced as powdered pitch.
 4. Theprocess of claim 1 wherein the pitch is introduced as pelletized pitch.5. The process of claim 1 wherein the pitch is a synthetic mesophase orisotropic pitch.
 6. The process of claim 1 wherein the pitch is apetroleum derived mesophase or isotropic pitch.
 7. The process of claim1 wherein the pitch is a coal-derived mesophase or isotropic pitch. 8.The process of claim 1 wherein the pitch is a blend of pitches selectedfrom the group consisting of synthetic mesophase or isotropic pitch,petroleum derived mesophase or isotropic pitch, and coal derivedmesophase or isotropic pitch.
 9. The process of claim 1 wherein thepitch is a solvated pitch.
 10. The process of claim 1 wherein thepurging is effected by a vacuum step.
 11. The process of claim 1 whereinthe purging is effected by an inert fluid.
 12. The process of claim 1wherein the vacuum is applied at less than 1 torr.
 13. The process ofclaim 1 wherein nitrogen is introduced as the inert fluid.
 14. Theprocess of claim 1 wherein the pitch is heated to a temperature in therange of about 500° C. to about 1000° C. to coke the pitch.
 15. Theprocess of claim 1 wherein the pitch is heated to a temperature of about800° C. to coke the pitch.
 16. The process of claim 1 wherein thetemperature to coke the pitch is raised at a rate of no greater than 5°C. per minute.
 17. The process of claim 1 wherein the pitch is soaked atthe coking temperature for at least 15 minutes to effect the coking. 18.The process of claim 1 wherein the pitch is heated to a temperature ofabout 630° C. to coke the pitch.
 19. The process of claim 1 wherein thepitch is heated to a temperature of about 50° C. to about 100° C. tocoalesce the pitch.
 20. The process of claim 1 where the foam is cooledat a rate of approximately 1.5° C./min with the release of pressure at arate of approximately 2 psi/min.
 21. The process of claim 1 furtherincluding the step of densifying the foam.
 22. A carbon foam produced asproduced by the process of claim 1 .
 23. A carbon foam as produced bythe process of claim 1 with a smooth face sheet.
 24. A process ofproducing carbon foam comprising: selecting an appropriate mold shapeand a mold composed of a material that the molten pitch does not wet;introducing pitch to an appropriate level in the mold; purging the airfrom the mold; heating the pitch to a temperature sufficient to coalescethe pitch into a liquid; releasing the vacuum and applying an inertfluid at a static pressure up to about 1000 psi; heating the pitch to atemperature sufficient to coke the pitch; and cooling the foam to roomtemperature with a simultaneous release of pressure.
 25. The process ofclaim 24 wherein the pitch is introduced as granulated pitch.
 26. Theprocess of claim 24 wherein the pitch is introduced as powdered pitch.27. The process of claim 24 wherein the pitch is introduced aspelletized pitch.
 28. The process of claim 24 where in the pitch is asynthetic mesophase or isotropic pitch.
 29. The process of claim 24where in the pitch is a petroleum-derived mesophase pitch.
 30. Theprocess of claim 24 where in the pitch is a coal-derived mesophasepitch.
 31. The process of claim 24 wherein the mold is purged by avacuum applied at less than 1 torr.
 32. The process of claim 24 whereinthe mold is purged by an inert fluid before heating.
 33. A process ofproducing carbon foam core composite comprising: selecting anappropriate mold shape; introducing pitch to an appropriate level in amold; purging air from the mold; heating the pitch to a temperaturesufficient to coalesce the pitch into a liquid; releasing the vacuum andapplying an inert fluid at a static pressure up to above 1000 psi;heating the pitch to a temperature sufficient to cause gases to evolveand foam the pitch; heating the pitch to a temperature sufficient tocoke the pitch; cooling the foam to room temperature with a simultaneousrelease of pressure; placing facesheets on the opposite sides of thecarbon foam; and adhering the facesheets to the carbon foam.
 34. Theprocess of claim 33 wherein the adhering of the facesheets to the carbonfoam is effected by a molding step.
 35. The process of claim 33 whereinthe adhering of the facesheets to the carbon foam is effected by acoating material.
 36. A composite carbon foam product produced by theprocess of claim 33 .